Allow use of ppx in dune #27187

Job	Run time
Coverage (4.14.x)	5m 30s
Coq 8.16.1	10m 6s
Build (macos-latest, 4.14.x)	4m 44s
Create local opam switch (macos-latest, 5)	7m 10s
Build (ubuntu-latest, 4.14.x)	4m 36s
MSVC 4.14.0 / windows_x86	7m 10s
Create local opam switch (macos-latest, 4.14)	6m 58s
Documentation	35s
Build (windows-latest, 4.14.x)	3m 15s
MSVC 4.14.0 / windows_x86_64	7m 11s
Create local opam switch (ubuntu-latest, 5)	7m 13s
Build (ocaml-variants.5.3.0+trunk, ubuntu-latest, true)	4m 55s
Create local opam switch (ubuntu-latest, 4.14)	7m 11s
Build (5.1.x, ubuntu-latest, true)	4m 27s
Format	2m 15s
Build monorepo benchmark docker image	2m 55s
Build (5.1.x, macos-latest, true)	5m 49s
Nix (macos-latest)	1m 58s
Build (4.14.x, macos-13, true)	9m 49s
Nix (ubuntu-latest)	55s
Build (4.13.x, ubuntu-latest, true)	4m 59s
Build (4.08.x, ubuntu-latest, true)	4m 37s
Build (4.04.x, ubuntu-latest, true, true)	6m 19s
Build (4.02.x, ubuntu-latest, true)	5m 28s
	2h 6m 5s

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